Liquid velocity sensors are utilized for a number of differing applications. In the marine industry, especially on recreational marine vessels such as racing yachts, it is desirable to have an extremely fast accurate and linear fluid velocity measurement system which maintains its accuracy over a wide range of velocities. When operating recreational marine vessels such as sailing yachts in conditions of high wind, it is highly desirable to obtain the optimum velocity made good (VMG) from the vessel that can be obtained at any wind condition. Many different vessel adjustments can be made to enhance boat velocity through the water for any wind condition but especially under conditions of low or light wind it is quite difficult to determine that the best velocity is being obtained. It is desirable therefore to provide a fluid velocity indicator that is extremely accurate and quite linear at all conditions of fluid velocity. Upon making an adjustment in the sail or rigging of a vessel it is desirable that the resulting velocity change of the vessel be displayed as soon as possible. This enables the crew of a racing vessel to quickly obtain the best vessel speed (VMG) under any conditions of wind.
For application as speed or velocity sensors in marine vessels, paddle wheel type boat speed sensors have been found reasonably acceptable. The main problem with paddle wheel type fluid velocity sensors is the inability to provide a speed sensor which is accurate and linear in its signal production over a wide range of vessel speeds. One paddle wheel type fluid flow meter sensor that has been utilized as a speed or fluid velocity sensor for marine vessels is constructed in accordance with U.S. Pat. Nos. 4,173,144 and 4,440,030 of Pounder. A vessel speed sensor so constructed however but utilizing permanent magnets within the paddle wheel for generating analog detectable signals which require further signal processing has been found appropriately sensitive and linear only at relatively high fluid velocities. At low fluid velocity the boat speed sensor becomes substantially non-linear and is therefore quite inaccurate. It is desirable therefore to provide a paddle wheel type fluid velocity sensor which is directly digital and effectively provides a linear response at a wide range of fluid velocities, especially including low velocity. It is also desirable to provide a paddle wheel fluid velocity sensor which provides a significant volume of data for each revolution thereof to thus enhance the sensitivity and accuracy of the fluid velocity sensor.
Paddle wheel type velocity sensors are also capable of application as flow sensors. For example, U.S. Pat. No. 4,440,030 is entitled "Fluid Flow Meter" because of its principal application as a fluid flow meter for measurement of the velocity of fluid flow in various flow conduits. U.S. Pat. No. 4,173,144 is directed to a low flow rate transducer construction but requires a housing having a cylindrical paddle wheel chamber. In this form it is not applicable for use as a velocity or speed sensor for marine vessels. It is desirable therefore to provide a fluid flow meter including a paddle wheel type fluid flow sensor which has effective linearity at a wide range of fluid velocities for accuracy of fluid flow measurement even at very low fluid velocities.